A vessel comprises different rotating parts that pass through openings in the vessel or in equipment relating to the vessel and that must be sealed against a medium e.g. sea water or oil etc. in said opening.
A vessel provided with a propulsion unit comprises at least two positions where a rotating part passing through an opening must be sealed against a medium. A propulsion unit comprises a hollow strut with an upper portion and a lower portion. The upper portion of the strut forms a support arm supporting the lower portion of the strut.
The upper portion of the strut of the propulsion unit is connected to an upper block. The upper block passes through a first opening formed in a bottom of a vessel from a first outer bottom to a second inner bottom of the vessel. The upper block is rotatably attached with a slewing bearing to the hull of the vessel. The upper block has normally a generally cylindrical from. The upper block could instead of being a separate part be formed by an upper end portion of the upper portion of the strut. A slewing seal positioned under the slewing bearing forms the seal between sea water and the interior of the hull of the vessel and between the oil of the slewing bearing and the sea water. This is the first position where a rotating part i.e. the upper block is sealed in the first opening against sea water.
The lower portion of the strut forms a longitudinal compartment comprising a first electric motor connected with a first shaft to a propeller positioned outside the lower portion of the strut. The first shaft is rotatably supported with bearings within the lower portion of the strut. The first shaft passes through a second opening in an end wall at an aft end of the lower portion of the strut and is sealed with a seal against sea water in the second opening. The seal prevents also oil from the shaft bearing from penetrating into the sea water. This is the second position where a rotating part i.e. the first shaft is sealed in the second opening against a medium.
There is a need to relocate the slewing seal and the shaft seal from time to time. The time interval for the relocation might be different for the slewing seal and the shaft seal. This is due to the wear of the liner on the outer surface of the rotating part at the points where the lip portions of the seal parts in the seal rings act. The lip parts of the seal parts in the seal rings will again act on a fresh surface of the liner after the axial relocation of the seal.